The preparation of alkoxylated compounds is well known. Typically, the method used to prepare alkoxylated compounds produces a mixture of products that is less than ideal. This is especially in the case in the preparation of alkoxylated, nitrogen compounds such as alkanolamines.
For example, alkanolamines, such as monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) are often prepared by reacting ethylene oxide with ammonia. The resulting product is a mixture of MEA, DEA, and TEA. While changing the stoichiometry of the reactants can vary the ratio of these amines in the final product mixture, the reaction is still not sufficiently selective to produce a high level of DEA.
Various approaches have been used to overcome this problem. For example, U.S. Pat. No. 4,264,776 (to Monsanto), Apr. 28, 1981, discloses the catalytic oxidation of tertiary amines with oxygen to form secondary amines in the presence of an active carbon catalyst. An example is provided which treats TEA over active carbon at 115° C. in the presence of oxygen with 60% conversion to DEA.
U.S. Pat. No. 4,328,370 (to TDCC), May 4, 1982, discloses the use of hydrogenation catalysts (Pd, Pt, Rh, Ru) at super-atmospheric pressure under anhydrous conditions. For example, TEA is treated with ammonia in the presence of Pd/C or Pd/Al2O3, optionally in the presence of hydrogen, at 200-300° C. to give MEA and DEA.
U.S. Pat. No. 6,469,214 B2 (to BASF) Oct. 22, 2002, discloses the preparation of DEA from a mixture of MEA and TEA in the presence of a strong base and, optionally, ammonia. The preferred strong bases are alkali metal and alkaline earth metal hydroxides, or an alkali metal alkoxide.
WO 2007/093514 A1 (to BASF), Aug. 23, 2007, discloses the conversion of monoethylene glycol into MEA and DEA via a reductive amination.
U.S. Pat. No. 6,169,207 (to Nippon Shokubai Kagaku Kogyo (NSKK)), 2001, discloses selective ethoxylation.
There remains a need for a more efficient method for the preparation of, for example, secondary alkanolamines.